internal: Borrow text of immutable syntax node

[iDawer]

In rust-analyzer/rowan#101 rowan::SyntaxNode::green returns Cow<'_, GreenNodeData>. It returns borrow of green node of immutable syntax tree node.
Using this we can return borrowed text from ast::Name::text.

However now it allocates in case of mutable syntax trees. (see next comment)

The idea comes from rust-analyzer/rowan#100 (comment)

[iDawer]

Replaced Cow<str> with cow-like TokenText:

pub enum TokenText<'a> {
    Borrowed(&'a str),
    Owned(GreenToken)
}

Though, it does not implement ToOwned.

The draft is waiting for:

• Landing of Borrow nodes of immutable syntax trees rust-analyzer/rowan#101

[matklad]

would be interesting to get some benchmakrs here. You can run cargo xtask bb baseline / cargo xtask bb cow to prepare two test binaries, and /target/rust-analyzer-last-cow -q analysis-stats --memory-usage . to run a simple bench.

[iDawer]

With cpupower frequency-set -g performance applied:
master 27e80e9 vs this f316163

[dawer@iPC rust-analyzer]$ ./target/rust-analyzer-baseline_27e80e9 -q analysis-stats --memory-usage .
Database loaded:     946.71ms, 283minstr, 86mb
  crates: 34, mods: 649, decls: 12591, fns: 9924
Item Collection:     19.01s, 77ginstr, 288mb
  exprs: 278045, ??ty: 2512 (0%), ?ty: 1870 (0%), !ty: 1064
Inference:           46.72s, 120ginstr, 441mb
Total:               65.73s, 197ginstr, 729mb

[dawer@iPC rust-analyzer]$ ./target/rust-analyzer-cow_f316163 -q analysis-stats --memory-usage .
Database loaded:     949.80ms, 283minstr, 86mb
  crates: 34, mods: 649, decls: 12591, fns: 9924
Item Collection:     19.04s, 77ginstr, 288mb
  exprs: 278045, ??ty: 2512 (0%), ?ty: 1870 (0%), !ty: 1064
Inference:           46.91s, 120ginstr, 441mb
Total:               65.95s, 197ginstr, 729mb

[matklad]

LGTM, @iDawer can you rebase?

bors d+

[bors]

✌️ iDawer can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[iDawer]

Hmm, version 0.13.0-pre.5 introduced breaking change in "pre" version, is it ok?
Currently, rowan dependency is pinned on "=0.13.0-pre.3" (#8551) because of this.
I'm uncertain, shouldn't we bump rowan's minor version with the change + revert the change in 0.13.0-pre.6 to be in line with semantic versioning?

[matklad]

Breaking changes in pre version are OK -- that's exactly what makes pre versions useful!

[iDawer]

I left rowan version pinned rowan = "=0.13.0-pre.5"

bors r+

[iDawer]

bors r+

[Veykril]

bors retry

[bors]

Build succeeded:

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